Fire and smoke detector



Sept. 30, 1969 A A JAFFE ET AL 3,470,551

FIRE AND SMOKE DETECTOR Filed Dec. 2, 1965 A 2 Sheets-Sheet l OOOO O OOOOO @OOO O OOOO OOOOO OOOOO Sept. 30, 1969 A. A. JAFFE ET AL FRE AND vSMOKE DETECTOR United States Patent() 3,470,551 FIRE AND SMKE DETECTOR Abram Aubrey Jaffe and Eliahu Nadav, Jerusalem, Israel, assignors to Yissum Research Development Company, Jerusalem, Israel, a company of Israel Filed Dec. 2, 1965, Ser. No. 511,100 Claims priority, application Israel, Dec. 27, 1964, 2 73 2,6 Int. Cl. G08b 21 00 U.S. Cl. 340-237 4 Claims ABSTRACT F THE DISCLOSURE This invention relates to a tire and smoke detector and more particularly to a lire and smoke detector the operation of which is dependent upon the detection of the net electrical charge carried by smoke and combustion products from tires.

Heretofore, fire detecting apparatus which depend upon detection of the by-products of combustion have included smoke detectors embodying optical measuring apparatus or gas detectors employing chemicals to detect specific gases, such as carbon monoxide or carbon dioxide, usually formed in the combustion process. These prior device have been relatively complicated, as well as unsuitable or unreliable for many applications, and have required considerable supervision and maintenance, such .as the periodic replacement of exhausted chemicals or parts.

More recent fire and smoke detectors which depend upon detection of the by-products of combustion have included ionization chambers having at least one'pair of electrodes spaced therein. Such electrodes have been impressed with a relatively high potential therebetween to establish predetermined conductivity characteristics of the air between the electrodes. Recognizing that the byproducts of combustion may contain ionized molecules or particles, the presence of such ionized particles within the ionization chamber increases the conductivity within the chamber, which increase of conductivity may be detected, amplified and utilized to activate suitable alarm and/or fire fighting equipment. Recognizing also that smoke particles may sometimes occur without ionized air particles or molecules, these more recent iire and smoke detectors have provided a second ionization chamber which includes a second pair of voltage impressed spaced electrodes to shield the interior of the second chamber against the admission of extraneous ionized air particles. Provided within the second chamber is a quantity of radioactive material the radiation of which imparts normal conductivity characteristics to the space between the electrodes. The presence of smoke particles in the chamber impedes the progress of the alpha-radiation from the radioactive material and thereby reduces the amount of ionization of the air produced by such radioactive material. The reduction of conductivity characteristics within the second chamber may be electrically sensed, amplified and utilized to activate suitable alarm and/or lire lighting apparatus.

Patented Sept. 30, 1969 An example of the ionization chamber technique of detecting smoke and combustion by-products may be seen in United States Patent 2,4008,05l issued to K. O. Donelian on Sept. 24, 1946.

'I'he above described prior art re and smoke detectors, as illustrated by the Donelian patent, suffer from several disadvantages which the instant invention effectively eliminates. lSpecifically, a device such as that shown in the Donelian patent requires at least two ionization chambers, one of which detects an increase in conductivity between spaced electrodes due to the presence of ionized combustion products therebetween, and the second of which detects the influence of smoke particles on the normal conductivity characteristics established between a pair of spaced electrodes by a radioactive material. Secondly, both ionization chambers require that a relatively high voltage be impressed upon the spaced electrodes located therein; and thirdly, as is well known, the utilization of a radioactive material, especially those which emit alpha-particles, are a potential health hazard.

In contradistinction thereto, the instant invention is based on an effect which is quite different from the two effects utilized by such prior art devices as the Donelian patent. It is based on the fact that smoke and combustion products from lires carry a net electrical charge. Recognizing the fact that if a net electrical charge approaches an electrical conductor, an induced charge will be established on the surface of such conductor; the presence of smoke and combustion products from tire may be simply detected by the eletcrical observation of such induced charge on a single electrical conductor. Thus, where the prior art detectors, illustrative by the Donelian patent, require separate ionization chambers to detect (1) the presence of ionized combustion products, and (2) the presence of non-ionized smoke particles, the instant invention 4materially simplifies lire detection by electrically detecting the presence of an induced charge on a single conductor.

The advantages derived from the detection of net electrical charge of combustion products may be summarized as follows. A single detector consisting of a single electrode is possible and neither an ionization nor deionization chamber is required. Similarly, where the ionization and the de-ionization chambers of the prior art devices require that relatively high voltages (for example, volts) be impressed upon the spaced apart electrodes located therein, the instant invention requires neither the pairs of electrodes nor the potential impressed thereon. Furthermore, the instant invention completely eliminates the necessity for a radioactive source which, as noted before, presents a potential health hazard in the detectors of the prior art.

As a further advantage, it may be appreciated that the single electrode of the instant invention may be made of any shape to provide protection for large and/ or irregular areas while the double ionization chambered device of the prior art is relatively complex and, therefore, does not lend itself to various shapes and sizes.

Accordingly, 4it is an object of the instant invention to provide a lire and smoke detector, the operation of which is dependent upon the fact that smoke and combustion products from fire carry a net electrical charge which may be sensed and amplified to activate suitable alarm and/or iire lighting apparatus.

It is another object of the instant invention to provide apparatus# for detecting smoke and combustion products from lires comprising sensing means for producing a signal indicative of the presence of a net electrical charge carried by smoke and combustion products from fires; rand amplifier means connected to said sensing means for amplitiying said signal.

It is another object of the instant invention to provide a fire and smoke detector which eliminates the relatively complex arrangements prevalent in the prior art.

Still'another object of the instant invention is to provide a fire and smoke detector which electrically detects the presence of an induced charge on an electrode, which induced charge has been established by the approach of the net electrical charge carried by smoke and combustion products from fires.

Yet another object of the instant invention is to provide a fire and smoke detector the simplicity of which permits great flexibility with respect to size and shape.

Other objects and a fuller understanding of the instant invention may be had by referring to the following specification and drawings, in which:

FIGURE 1 is a somewhat schematic diagram of a fire land smoke detector constructed in accordance with the teachings of the instant invention;

FIGURE 2 is an electrical circuit diagram of an amplifier which may operate in conjunction with the fire and smoke detector -of the instant invention; and

FIGURE 3 is an electrical circuit diagram of an -alarm device which may be utilized in conjunction with the amplifier of FIGURE 2.

Referring to FIGURE 1, there -is shown an illustrative embodiment of the instant invention. The detector comprises a sensing element 12, which may be any metal electrode (i.e., electrically conducting material), preferably mesh or perforated, and hollow inside. The sensing element 12 may be virtually of any shape, for example, -a long cylinder extending over a number of yards, or alternatively, may comprise a large, fiat box or sheet to give protection over a large area, such as a ceiling or roof. It is to be understood that the flexibility of shape which the simplicity of the instant invention facilitates represents an important feature of the instant invention in that the invention may be suitably adapted to provide adequate fire protection in var-ions sized and/or irregularly shaped rooms or areas.

Sensing element 12 is supported by an insulator 13 of good electrical insulating properties, for example, polytetrafiuoroethylene, and is enclosed by a grounded shield 11, the purpose of which is to screen the sensing element `1 2 from any external charges or fields while simultaneously allowing the flow of smoke or combustion products from fires to flow readily therethrough. The shield 11 consists of electrically conducting material preferably in the form of wire mesh or perforated sheet. Although grounded shield 11 is shown as a single layer of metal in FIGURE 1, it is to be understood that more effective electrical screening may be obtained by using several layers of such material.

The shape of the grounded shield =11 should conform to, but be larger than, the shape of the sensing element 12. Thus, if the sensing element 12 were chosen as a long cylinder, the grounded shield 11 would consist of a coaxial cylinder, or series of cylinders, which enclose the sensing element.

An electrical connection is made by an insulated lead through 14 which may consist of a coaxial connector of conventional type, to an electronic amplifier 15. As will be explained in greater detail, amplifier 15 may be of either a voltage sensitive or charge sensitive type. If a charge sensitive amplifier is used the sensing element may be extended up to va limit such that its electrical capacity is approximately equal to the effective input capacity of the amplifier, without serious loss of sensitivity, Alternatively a number of smaller sensing elements may be connected to a single amplifier. The output of amplifier 15 energizes a relay 16 with one or more pairs of electrical contacts 17 therein being controlled by energzation of the relay 16 to operate any desirable alarm device I18 -and/or automatic fire extinguishing apparatus 19.

It is to be understood that the instant invention may be combined with a sampling system, for example, consisting of a fan and air ducts, to sample lover a large area.

The operation of the fire and smoke detector of the instant invention will now be described with respect to FIGURE 1.

Recognizing that smoke and combustion products from fire carry a net electrical charge, the entrance of such combustion products through the perforated, grounded shield 11 and the approach of such products to the immediate vicinity of the sensing element 12, will induce a charge on the surface of sensing element 12. As noted previously, the creation of the induced charge on the surface of sensing element 12 may be observed in changes of electrical potential of the sensing element or by detecting currents flowing from or into such conductor if it is connected to a fixed potential, such as ground. Assuming that amplifier 15 is of a charge sensitive type, (an example of such amplifier being illustrated in FIGURE 2), it will be apparent that the ow of current between the sensing element 12 and ground, will be amplified by amplifier 15 to energize the coil of relay -16 to close one or more pairs of contacts 17 and activate alarm and/or fire lighting apparatus 18 and 19.

Referring to FIGURES 2 and 3, there is shown a schematic diagram of an amplifier and alarm circuit which may be used in conjunction with the sensing apparatus described above. It is to be understood, however, that the particular amplifier and -alarm unit shown and described is merely presented as an illustrative embodiment of the instant invention and that the instant invention is in no way intended to be limited to such circuitry.

Without going into the details of the circuit presented in FIGURE 2 (since all circuit elements have been appropriately identified), it is noted that sensing element 12 which is surrounded by a grounded shield 11 represents the input to the field effect transistor Q1 of the first stage of the charge sensitive amplifier 15. The output from amplifier 15 represents the input to the alarm unit, the output coil RL1 of which is energized to close multiple contacts 17 to activate the alarm and/or fire lighting equipment.

Thus, there has been described a fire and smoke detector, the operation of which is dependent upon the induction of change on a single electrode, which induced charge has been established by the presence of the net electrical charge carried by smoke and combustion products from fires. It is seen that the instant invention represents a significant advancement in terms of simplicity of consturction and operation over prior art devices while at the same time the liexibility inherent in the instant invention lends itself to the maximum protection of large and/or odd-shaped areas.

What is claimed is:

1. Apparatus for detecting smoke and combustion products comprising an electrical conductor, a surface of which has an induced charge established thereon when approached by the net electrical charge carried by smoke and combustion products;

detection means for detecting the creation of said induced charge on said conductor; and shield means surrounding said electrical conductor for screening said electrical conductor from external charges and electric fields while at the same time permitting the flow of smoke and combustion products therethrough.

2. The apparatus of claim 1, lwherein said detecting means includes:

an amplifier for amplifying a signal which represents the establishment of said induced charge on said electrical conductor; and

alarm means responsive to said amplifier for signifying the presence of smoke and combustion products within said shield means.

3. The apparatus of claim 1, wherein said shield means 5 6 comprises at least one layer of perforated conducting 2,815,483 12/ 1957 Kaufman 324-72 material. i 2,820,947 1/ 1958 Gunn 324-72 4. The apparatus Of Claim 3, wherein Sald perforated 2,994,035 7 /1961 Feifel et aL 324 32 XR conducting material is electrically grounded.

References Cited 5 JOHN W. CALDWELL, Pnmary Exammer 2,408,051 9/1946 Donelian 340-237 Us C1 XR. 2,491,445 12/ 1949 Cunningham et al.

2,556,458 l6/1951 Webster. 10 317448'5262 

